End stops for dual end stop actuator and method

ABSTRACT

A dual end stop is provided for setting precise open and closed positions for the valve to which the pneumatic actuator is attached. In a preferred embodiment, a stop assembly housing contains two stop adjustment bolts as well as a cam that defines first and second stop surfaces. The stop assembly housing is preferably mounted to the actuator housing outside of the pressurized zone contained by the actuator housing. The stop bolts and associated threaded apertures are designed for minimum overhang of the stop bolts to provide more support. The stop assembly housing not only preferably houses the stop assembly components but also preferably serves as an adaptor plate for the various valves to which the actuator may be mounted.

This application is a continuation of U.S. patent application Ser. No.09/736,618 filed Dec. 14, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to rotary valve actuators and,more particularly, to apparatus and methods for a dual end stop actuatoradjustment.

2. Description of the Background

Actuators, such as a piston activated pneumatic actuators, are wellknown in the prior art for controlling valves between an open positionand a closed position. An exemplary and highly compact configuration fora pneumatic actuator is shown in U.S. Pat. No. 4,354,424, issued Oct.19, 1982, to Sven Nordlund, which is hereby incorporated herein byreference. In that actuator, each actuator piston is provided with arack having teeth thereon to engage corresponding teeth of an operatingelement. The rack includes a recess for receiving a first spring thatproduces a return force on the piston. The recess extends substantiallyinto the rack of the piston. A second shorter spring is provided withina central portion of each actuator piston. Thus, one spring in eachpiston is offset from the center and is longer than the other spring.The offset, longer spring provides a solution to a basic problem ofcompact spring return actuators. Prior to this invention, such actuatorsdid not consistently have sufficient spring force to completely closethe valve.

Many valves have requirements for drift adjustments that adjust thevalve position to an exactly open position and/or an exactly closedposition. For these cases, if the valve is not adjusted correctly, theflow path through the valve may not be completely open or accuratelyclosed due to an offset in the valve control element. If the flow pathis not accurately controlled, then the system efficiency may be reduced,failures may occur, and maintenance costs may increase. Thus, it isoften desirable to have a drift adjustment, or end stop adjustment, foradjusting the valve element for a more precise desired open and closedposition. A dual end stop adjustment in the actuator, which is known inthe prior art, permits adjustment of the open and closed position forthe valve by adjusting the extent of movement of the valve actuatorcontrol element. For a rotational valve actuator element, it is knownthat a dual end stop adjustment has been used to provide two rotationalstop positions for the rotational valve element.

The dual end stop adjustment may be used for many thousands of valveopenings and valve closings over the lifetime of operation. Prior artend stop adjustments have a tendency change in drift or stop adjustmentover time due to many openings and closings to thereby possibly causedeleterious operation of the valve system, significantly increasemaintenance costs, and decrease overall system efficiency.

Prior art pneumatic actuators provide that the dual stop adjustment issealed within the pressure zone of the actuator housing. Thus, thepressurized air, fluid, gas, and the like, used to activate the valve ispresent at the stop adjustment mechanism. The inventor of the presentinvention considers this construction to be faulty and may lead tofailures and inaccuracies in the stop adjustment. One of the problems isthat the pressurized housing is typically limited in size available foractuator mounting so that for a desired piston size, the thickness ofthe housing is also accordingly limited. The adjustment bolts musttherefore extend through the relatively thin wall of the housing so asto be substantially unsupported along their length. Due to this lack ofsupport of the bolts and the relatively thin actuator wall, there is atendency for bending and warping in prior art actuators either in thebolts or the actuator wall. Thus, the thousands of openings and closingsof the valve may well lead to an unstable or effectively non-operationaldrift adjustment thereby potentially causing valve and/or valve systemmalfunctions.

The inventor has discovered other problems with existing dual stopadjustments for pneumatic actuators. One such problem concerns end stopbolts for engaging a stop surface wherein the flat head of the end stopbolt is subject to deformation, high spots, and the like which mayresult in an unstable drift adjustment. Another problem discovered bythe inventor relates to the mounting or adaptor plate used to secure theactuator to various types of valves which plates thereby adapt theactuator to the particular type of valve. Prior art mounting plates aresupported and positioned by bolts that are subject to offsets, bending,and warping which leads to inaccuracies in the dual end stop adjustmentsas well as the connection to the valve which may require high accuracyto standards, such as for instance, ISO standards. Another discoveredproblem relates to the machining cost of drilling numerous holes in themounting plates for support bolts. Depending on the location of thebolts, this can result in additional machining operations so that,according to the inventor, it would be desirable to achieve additionalreliability and accuracy with a reduced number of mounting bolt holes.Yet another discovered problem relates to bending and offsets of therotary drive shaft element due to torque applied to the rotary driveshaft element by the stop adjustment. Yet other discovered problemsrelate to stress in the mechanical supports for the dual end stopadjustment.

Consequently, there remains a need for a more reliable, consistent, andstable dual end stop adjustment that solves the above-listed unaddressedproblems and other problems of prior art pneumatic actuator dual endstop adjustment mechanisms. Those skilled in the art have long soughtand will appreciate the present invention which provides solutions tothese and other problems.

SUMMARY OF THE INVENTION

The present invention was designed to provide more accurate and reliableoperation of a pneumatic actuator to thereby more accurately controlvalve openings and closings over a lifetime of operation and to avoiddeleterious changes that may greatly increase maintenance costs andreduce efficiency of a system of valves.

Therefore, it is an object of the present invention to provide animproved pneumatic actuator.

Another object of the present invention is to provide an improved dualend stop adjustment for a pneumatic actuator.

Yet another object of the present invention is to provide a dual endstop adjustment that does not vary in adjustment even after many, many,thousands of openings and closings of the valve.

These and other objects, features, and advantages of the presentinvention will become apparent from the drawings, the descriptions givenherein, and the appended claims.

Therefore, the present invention may provide for a dual end stop for apneumatic actuator wherein the pneumatic actuator comprises an actuatorhousing which has a zone for pressure containment. A rotary driveelement is mounted for rotation within the actuator housing. Theapparatus comprises elements such as a stop element mounted to therotary drive element for rotation therewith. The stop element has afirst stop surface and a second stop surface. The stop element maypreferably be positioned outside of the zone for pressure containment. Afirst stop member is utilized for engaging the first stop surface. Thefirst stop member, in a preferred embodiment, may be mounted outside ofthe zone for pressure containment. A second stop member is also utilizedfor engaging the second stop surface and the second stop member may alsopreferably be mounted outside of the zone for pressure containment.

In a preferred embodiment, a first bearing is mounted on the rotarydrive element on a first side of the stop element. A second bearing ismounted on a second side of the stop member opposite to the first side.In a presently preferred embodiment, the first bearing is mounted in theactuator housing adjacent a stop assembly housing and the second bearingis mounted in the stop assembly housing.

The stop assembly housing may preferably be provided defining anaperture therein.

The stop assembly housing may preferably be mounted to the actuatorhousing and the stop element may be positioned within the stop assemblyhousing. In a preferred embodiment, a first threaded portion for thefirst and/or second stop member engages and extends into a receptaclesuch that more than eighty percent of the first threaded portionextending into the receptacle may be threadably engaged so as to besupported within the receptacle.

In another aspect of the invention, a rounded, convex, or tapering endof the first and/or second stop member is engagable with the first stopsurface so as to provide a defined point contact therewith.

The present invention also comprises a method forassembling/construction and may comprise steps such as providing therotary drive element with a first stop surface and a second stop surfacesuch that the first stop surface and the second stop surface arepreferably positioned outside of the zone for pressure containment.Other steps may preferably include providing a first stop member forengaging the first stop surface to stop the rotary drive element in afirst rotational position wherein the first stop member may be moveablerelative to the stop surface for adjusting the first rotationalposition. Another step comprises providing a second stop member forengaging the second stop surface to stop the rotary drive element in asecond rotational position wherein the second stop member may bemoveable relative to the stop surface for adjusting the secondrotational position.

Additional steps may include one or more of the following: mounting thefirst stop member and the second stop member within a stop assemblyhousing, providing an aperture within the stop assembly housing,providing a first radiuused section as part of the aperture adjacent thefirst stop member, providing a rounded end surface for the first stopmember such that the rounded end surface is engagable with the firststop surface, and/or providing support for the first stop member suchthat the stop member is threadably supported at a position closelyadjacent the rounded end.

In another preferred embodiment, a stop assembly housing may be sized tofit into a recess in the actuator housing. The stop assembly housingdefines an aperture therein. The first stop member may be mounted withinthe stop assembly housing such that the first stop member ispositionally adjustable and/or the second stop member may also bemounted within the stop assembly housing such that the second stopmember is positionally adjustable.

The stop assembly housing is preferably machined for accuracy to adesired size to thereby mate to the recess and the recess in theactuator housing is also preferably machined to a size for receiving thestop assembly housing such that lateral movement of the stop assemblyhousing within the recess is prevented. In a presently preferredembodiment, the stop assembly housing and the recess are machined to atolerance of less than or equal to one-one thousandth of an inch for atight fit of the stop assembly housing within the recess.

In a preferred embodiment, an outer bearing for the rotary drive elementis mounted within the stop assembly housing such that the bearing may beon an opposite side of the stop element from the actuator housing. Aninner bearing may be provided for the rotary drive element mountedwithin the actuator housing adjacent the stop assembly housing.

A first relief groove may preferably be defined in the stop assemblyhousing adjacent the first convex head and/or a second relief groove maypreferably be defined in the stop assembly housing adjacent the secondconvex head.

This aspect of the method for making and/or construction and/or assemblyincludes machining a receptacle in the actuator housing and machiningsides of a stop assembly housing that is insertable into the receptacle.The steps of machining provide a tolerance between the receptacle andthe stop assembly housing such that the stop assembly housing isprevented from lateral movement.

For relieving stress in the stop assembly housing, a method of theinvention may include steps such as providing an aperture within thestop assembly housing for receiving the rotary drive, providing a firstgroove along the aperture, and providing a second groove along theaperture. The first stop adjustment member has a first end for engagingthe first stop surface and the second stop adjustment member has asecond end for engaging a second stop surface. Thus, more specificallythe method may include steps such as providing the first groove adjacentthe first end, and providing the second groove adjacent the second end.

The first end stop may preferably have a first tapering end which tapersto a first end point and the first tapering end surface may be engagablewith the first stop surface for point contact to thereby stop the rotarydrive element in a first rotational position. Likewise a second stopmember may have a second tapering end which tapers to a second endpoint. The second tapering end surface may be engagable with the secondstop surface for point contact to thereby stop the rotary drive elementin a second rotational position.

The present invention preferably utilizes bearings on either side of thestop element to prevent bending of the shaft due to forces applied tothe stop element. Thus, another method of the present invention maycomprise steps such as installing a first bearing for the rotary driveelement for supporting a first end of the rotary drive element,installing an outer bearing for the rotary drive element on an oppositeside of the rotary drive element from the first end such that the outerbearing is positioned adjacent the stop element, and installing an innerbearing for the rotary drive element adjacent the stop element on anopposite side of the stop element with respect to the outer bearing.

In a preferred embodiment, the first and second stop members aresupported along its length. Thus, the rotary actuator may define a firstthreaded elongate aperture for receiving the first elongate stop member.The first threaded aperture has a first outer opening for receiving thefirst elongate stop member. The first threaded elongate aperture has alength of threaded surface such that at least eighty percent of aportion of the first elongate member which extends from the first outeropening to the first end is threadably supported by the length ofthreaded surface. Moreover, the second elongate stop member may bethreaded so as to be moveable along an axis thereof for adjustablyengaging the second stop surface. The second elongate stop member has asecond end for engaging the second stop surface and the rotary actuatormay define a second threaded elongate aperture for receiving the secondelongate stop member. The second threaded aperture has a second outeropening for receiving the second elongate stop member. The secondthreaded elongate aperture has a length of threaded surface such that atleast eighty percent of a portion of the second elongate member whichextends from the second outer opening to the second end is threadablysupported by the length of threaded surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view, partially in section, of a stop assemblyhousing or adaptor plate in accord with the present invention shown in afirst rotational stop;

FIG. 2 is an elevational view, partially in section, of the stopassembly housing or adaptor plate of FIG. 1 in a second rotational stopposition;

FIG. 3 is an elevational view of a drive shaft mounted on a stopassembly housing in accord with the present invention;

FIG. 4 is an elevational view, partially in cross-section, alongsectional view lines 4—4 of the actuator shown in FIG. 5;

FIG. 5 is an elevational view of an actuator in accord with the presentinvention showing a stop assembly housing mounted to the actuatorhousing;

FIG. 6 is an elevational view, of an actuator with a drive shaftextending therethrough;

FIG. 7 is an elevational view, of an actuator with apertures in the stopassembly housing for adjustment of the stop positions; and

FIG. 8 is an elevational view, partially in section, of an alternativeembodiment stop assembly housing or adaptor plate in accord with thepresent invention.

While the present invention will be described in connection withpresently preferred embodiments, it will be understood that it is notintended to limit the invention to those embodiments. On the contrary,it is intended to cover all alternatives, modifications, and equivalentsincluded within the spirit of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and more particularly to FIG. 1, FIG. 2,and FIG. 8, there is shown a dual end stop 10 in accord with the presentinvention. Dual end stop 10 includes adaptor plate or stop assemblyhousing 12 which preferably is used to house the various dual end stopcomponents. Stop assembly housing 12 also acts as an adaptor plate toprovide a connection or mounting between actuator housing 14, shown inFIG. 4, FIG. 5, FIG. 6, and FIG. 7, and the various types of valves (notshown) which actuator 16 may be mounted to.

It is well known that actuator pistons (not shown) within actuatorhousing 14 may be used to activate rotary drive element 18, as shown inFIG. 3 and FIG. 4, to rotate in one direction, such as for a quarterturn, and then in the other direction by the same amount to therebyeffect opening and closing of the valve. Mounted to or monolithic withrotary drive element 18 is cam member 20 which acts as a stop elementaffixed to rotary drive element 18. Other shapes and configurations of astop element such as cam member 20 could also be used. Essentially, astop element or stop element assembly for dual end stop 10 shouldcomprise at least two stop surfaces, such as first stop surface 22 andsecond stop surface 23. Rotary drive element 18 and cam 20 then mayrotate between a first rotational position as shown in FIG. 1, and asecond rotational position as shown in FIG. 2. First and secondrotational positions of cam 20 correspond with an open/closed positionof the valve. For instance, the position of FIG. 1 may correspond to anopen valve and the position of FIG. 2 may correspond to a closed valve.

Dual end stop 10 may be used to accurately set the open and closedposition of the valve. For instance, in one embodiment a first stopmember such as stop adjustment bolt 24 and a second stop member such asadjustment bolt 26 may be adjusted by about plus and minus two andone-half degrees thereby providing a range of travel for a rotary driveof a quarter-turn actuator, such as rotary drive 18, and thecorresponding valve drive shaft, of a range of movement between abouteighty degrees and one hundred degrees. Depending on the actuator designand valve operational requirements, a somewhat greater range ofadjustment for each stop member could be provided if desired, forinstance, about plus and minus five degrees. For convenience ofoperation, stop adjustment bolts 24 and 26 are threaded bolts althoughother adjustable members could be used that may include gears, ratchets,and the like that may provide the sufficiently fine adjustments requiredto set the stops. In a presently preferred embodiment, lock nuts 28 and30 are used to lock stop adjustment bolts in position to prevent furtherrotation once the desired stop settings are made. In another embodimentof the invention as shown in FIG. 8, adjustment bolts 24A and 26A areprovided in a manner such that the adjustments are tamper resistant.Adjustment bolts 24A and 26A are not immediately available foradjustment thereby reducing the likelihood that inadvertent adjustmentmight be made by personnel. In this case, in line lock bolts 27 and 29are used to lock the position of adjustment bolts 24A and 26A,respectively. Lock bolts 27 and 29 cannot be used to make adjustments.Preferably, lock bolts 27 and 29 extend only slightly, if at all, fromstop assembly housing 12 to further discourage unneeded adjustments.

A preferred embodiment of the present invention utilizes severaldifferent special features to prevent any deformation of stop adjustmentbolts 24 and 26 and/or their mounting within stop assembly housing 12.Stop adjustment bolts 24 and 26 are preferably manufactured from hightensile steel.

Preferably stop adjustment bolts 24 and 26 and the correspondingapertures in which they are inserted, such as threaded apertures 32 and34, are designed for full thread engagement and minimum overhang of stopadjustment bolts 24 and 26 with respect to threaded apertures 32 and 34.For those prior art actuators which may use a rotating stop member, suchas cam 20, full thread engagement is not provided. The prior artadjustment bolts extend through the pressurized zone for engaging thestop surfaces and are supported by the actuator housing which is oftenrequired to be compact for suitable mounting to the valve. Thus, thereis much less support for rotary stop members. On the other hand, thepresent invention preferably utilizes a separate stop assembly housingpreferably mounted outside of the pressurized zone wherein the stopassembly housing preferably doubles as the adaptor plate to provide acompact design. Therefore, adjustment bolts 24 and 26 as well asthreaded apertures 32 and 34 can preferably be designed for a minimumoverhang. As a general matter, the length of each adjustment bolt 24 and26, which extends from initial openings 36 and 38 at side wall 40 intostop adjustment housing 12, are threadably engaged for about 95% of thislength. Preferably at least 80% of this inserted length of eachadjustment bolt 24 and 26 is threadably engaged within threadedapertures 32 and 34. This additional support as compared to prior artdesigns eliminates any possible deformation or warping of either theadjustment bolts or their associated support structure to therebyprovide a more stable dual stop setting adjustment. Thus, the featuresproviding a separate stop assembly housing and of positioning the stopadjustment bolts outside of the pressurized zone within actuator housing14 for a pneumatic actuator, as further discussed in more detailhereinafter, has significant long term benefits related to more stablestop setting adjustments.

Another preferred feature of the present invention is spherical, convex,rounded, and/or tapered bolt heads or bolt ends 41 and 43 for eachrespective adjustment bolt 24 and 26. This structure is selected toproduce a defined contact point between first and second stop surfaces22 and 23 and the corresponding stop adjustment bolts 24 and 26. Byproviding a defined and centralized point contact, load distribution ismore uniform and less contact stress occurs on the mating faces. Thisdesign avoids the problems of prior art flat head bolts where there is apossibility of a random point contact associated with flat head boltsthat may result in a random contact face deformation leading to changingstop adjustment settings as well as random load distribution. Varioustapering designs for bolt ends 41 and 43 could be used although aspherical or convex profile is presently preferred.

Relief grooves 37 and 39 are provided adjacent bolt ends 41 and 43,respectively, to thereby reduce stress in plate or stop assembly housing12. The large blend radius of relief grooves 37 and 39 avoids stressconcentrations at the loaded bolt, the adjacent restraining bolt holes61 and 63, and the edge of stop bolt apertures 24 and 34. This in turnavoids the possibility of fatigue cracks propagating and ensures thepresent design has a superior fatigue life. In one finite analysis test,this design suggests the possibility of more than fifty million cyclesof repeated loadings without failure due to fatigue.

FIG. 3, FIG. 4, and FIG. 5 show the structural relationship betweenrotary shaft 18, actuator housing 14, and stop assembly housing 12.Referring to FIG. 3, a preferred rotary actuator shaft 18 is shown whichmay be rotated by gear teeth 42 and corresponding gear teeth on thepistons and/or piston shaft (not shown). In a preferred embodiment,rotary actuator shaft 18 is supported by three bearings including topbearing 44 which may preferably be a split bearing for supportingactuator shaft 18 on one side of actuator housing 14. Actuator shaft 18extends through pressurized zone 46 of actuator housing 14 and may, asshown in FIG. 4, extend through both sides of actuator housing 14.Actuator shaft 18 is sealed adjacent bearing 44 by seal 48, which maypreferably be an O-ring or elastomeric seal. Retaining clip 50 andcorresponding rubbing ring 52 may be used to secure the axial positionof actuator shaft 18 with respect to actuator housing 14 whilepermitting rotation of actuator shaft 18.

It will be understood that such terms as “up,” “down,” “vertical,” andthe like, are made with reference to the drawings and/or the earth andthat the devices may not be arranged in such positions at all timesdepending on variations in operation, transportation, mounting, and thelike. As well, the drawings are intended to describe the concepts of theinvention so that the presently preferred embodiments of the inventionwill be plainly disclosed to one of skill in the art but are notintended to be manufacturing level drawings or renditions of finalproducts and may include simplified conceptual views as desired foreasier and quicker understanding or explanation of the invention. Aswell, the relative size of the components may be greatly different fromthat shown.

Actuator shaft 18 is also supported by lower bearing 54 on the oppositeside of actuator housing 14 from bearing 44. Lower seal 56, which maypreferably be an elastomeric or O-ring seal, seals around actuator shaft18 adjacent to bearing 44. In a preferred embodiment, lower bearing 54is provided within actuator housing 14 adjacent to stop assembly housing12 and directly adjacent to one side of cam 20. Another bearing 58 ispreferably provided within stop assembly housing 12 on the opposite sideof cam 20 from lower bearing 54. The use of bearing 54 and bearing 58 oneither side of cam 20 ensures that no deflection of actuator shaft 18will occur even under maximum applied loads. Thus, forces applied to cam20 by stop adjustment members 24 and 26 against corresponding stopsurfaces 22 and 23 will not cause deflection of actuator shaft 18.

It will also be seen from FIG. 4 that stop assembly housing 12 ispreferably outside of pressure zone 46 which is sealed by seal 56. Thus,stop assembly housing 12 and the related components including stopadjustment members 24 and 26 as well as cam 20 with associated stopsurfaces 22 and 23 are all preferably positioned outside of pressurizedzone 46 contained within actuator housing 46. For safety and hygenicreasons, the stop surfaces and stop members are also preferably not opento ambience so fingers cannot be inserted therein and debris isprevented from reaching the stop surfaces and stop members.

In a preferred embodiment, stop assembly housing 12 is designed to besecurely supported within recess 59 in actuator housing 14. The fitbetween recess 59 and stop assembly housing 12 is preferably a verytight fit with tolerances in the range of about one-one thousandth of aninch. By providing a tight fit between stop assembly housing 12 andrecess 58 in actuator housing 14, the connection between thesecomponents is not only very accurate but also very strong and resiststorque, lateral movement, and other operating forces/stresses. In fact,in a preferred embodiment only two bolts such as bolts 60 and 62 arerequired because the only function of the bolts is to hold stop assemblyhousing 12 within recess 59. The position of stop housing 12 is alreadyfixed. Preferably both recess 59 and sides 40,64,66, and 68 of stopassembly housing 12 are milled rather than cast or molded to achieve thedesired accuracy of fit. In this manner, the adaptor plate, with orwithout the stop assembly, can be attached to the actuator housing for amore precise fit that can be made to conform with various standards suchas ISO standards that are used internationally for connecting actuatorsto valves such that the actuator and valve shafts align precisely. Dueto the costs of machining, the ability to use only two bolts to securestop assembly housing 12 to actuator housing 14 may result in reducedmachining costs, depending on the number and spacing of other holes,such as valve mounting holes 72,74,76, and 78 as well as alignment ring80. The valve mounting configuration on stop assembly housing 12 can bemade to suit for CEN, ISO, or customer valve mounting configurationrequirements. Shaft insert 82 will also suit standards such as ISO orcustomer valve requirements. The availability of three key slots 84,86,and 88 rather than just the two, in this case slots 84 and 88, allowsninety degree rotation of shaft insert 82 as desired for proper matingto the valve.

FIG. 6 and FIG. 7 show external views of actuator 16 including relativelocation of shaft 18, with valve position indicator 19 on one side ofactuator housing 14, and an adaptor plate which also preferablycomprises stop assembly housing 12 on the opposite side thereof.

It will be seen that various changes and alternatives may be used thatare contained within the spirit of the invention. For instance, themounting of the adaptor plate may be used whether or not the adaptorplate is also used as stop assembly housing 12 as is the presentlypreferred embodiment of the invention.

The foregoing disclosure and description of the invention isillustrative and explanatory thereof, and it will be appreciated bythose skilled in the art, that various changes in the size, shape andmaterials, the use of mechanical equivalents, as well as in the detailsof the illustrated construction or combinations of features of thevarious elements may be made without departing from the spirit of theinvention.

What is claimed is:
 1. A dual end stop for a valve actuator, said valveactuator comprising an actuator housing, said actuator housing having azone for pressure containment, a rotary drive element rotatably mountedwithin said actuator housing, a stop element having a first stop surfaceand a second stop surface, said dual end stop comprising: a first stopmember having a first end stop, said first end stop having a firsttapering end which tapers to a first end point, said first tapering endpoint being engageable with said first stop surface for point contact tothereby stop said rotary drive element in a first rotational position,said first stop member being moveable in a direction substantiallyperpendicular to a position of said first stop surface when said firststop member engages said first stop surface throughout an entire rangeof adjustment of first stop member with respect to said first stopsurface; and a second stop member having a second end stop, said secondend stop having a second tapering end which tapers to a second endpoint, said second tapering end point being engagable with said secondstop surface for point contact to thereby stop said rotary drive elementin a second rotational position. said second stop member being moveablein a direction substantially perpendicular to a position of said secondstop surface when said second stop member engages said second stopsurface throughout an entire range of adjustment of second stop memberwith respect to said second stop surface.
 2. The dual end stop of claim1, further comprising: a first position of said point contact betweensaid first tapering end point and said first stop surface, said firstposition remaining substantially constant over said entire range ofadjustment of first stop member with respect to said first stop surface.3. The dual end stop of claim 1, further comprising: a stop assemblyhousing mountable to said actuator housing, said first stop member andsaid second stop member being mountable within said stop assemblyhousing.
 4. The dual end stop of claim 3, further comprising: at leastone bearing for said rotary drive clement mounted within said stopassembly housing.
 5. The dual end stop of claim 1, wherein said firststop member and said second stop member are mounted outside of said zonefor pressure containment.
 6. A method for a dual end stop for a valveactuator, said valve actuator having an actuator housing, said actuatorhousing having a zone for pressure containment, a rotary drive elementrotatably mounted within said actuator housing, a stop clement having afirst stop surface and a second stop surface, said dual end stopcomprising: providing a first stop member with a first end stop having afirst tapering end surface, said first tapering end surface beingengagable with said first stop surface for slopping said rotary driveelement in a first rotational position; and providing a second stopmember with a second end stop having a second tapering end surface, saidsecond tapering end surface being engagable with said second stopsurface for stopping said rotary drive element in a second rotationalposition. providing that said first stop member is moveable along afirst adjustment path; providing that said second stop member is movablealong a second adjustment path; providing that said first adjustmentpath and said second adjustment path are parallel; providing that saidfirst adjustment path is substantially perpendicular to said first stopsurface when said first stop member engages said first stop member; andproviding that said second adjustment path is substantiallyperpendicular to said second stop surface when said second stop memberengages said second stop member.
 7. The method of claim 6, furthercomprising: forming a first tapering end surface with a convex profile,and forming said second tapering end surface with a convex profile. 8.The method of claim 6, further comprising: providing a stop assemblyhousing mountable to said actuator housing, and mounting said first stopmember and said second stop member within said stop assembly housing. 9.The method of claim 8, further comprising: mounting a bearing withinsaid stop assembly housing for supporting said rotary drive element. 10.The dual end stop of claim 6, further comprising: mounting said firststop member and said second stop member outside of said zone forpressure containment.